1. Field of the Invention
This invention relates to an improved antistatic agent, its preparation and use in polymeric shapes such as fibers and films.
2. Description of the Prior Art
Synthetic polymers when formed into such articles as molded objects or films are known to have a marked tendency to generate and accumulate electrostatic charges. When charged, these articles tend to accumulate concentrations of dirt and soil, which are unsightly in appearance and interfere with the end uses of the objects. When polymers are formed into fibers such as nylon and polyester the electrostatic charges create processing problems in fiber and yarn production such as poor package formation, filament and yarn breaks, and uneven spun yarn formation. In consumer use, carpeting made from synthetic fibers has a tendency to generate annoying shocks in cold, dry weather; while in apparel, the charged fabric clings uncomfortably to the wearer, shocks while the garment is being removed, and has an increased tendency to attract lint and soil.
In fiber production, topical antistats are used to decrease or eliminate the charges; such treatments have proven to be of little use in consumer applications because of their lack of permanency. Other methods used to decrease electrostatic charging in consumer applications of fibers include copolymerization of monomers containing ionizable radicals, surface grafted polymerization of monomers conferring antistatic properties to fibers, inclusion of metallic fibers in spun yarns, inclusion of carbon or metallic coated yarns or carbon-coated filaments within a bundle of continuous filaments, and incorporation of an antistatic additive in the matrix polymer used to melt spin fibers such as nylon and polyester. Incorporation of an additive into the polymer structure has proven to be a useful and flexible means of achieving antistatic effects.
It is taught in U.S. Pat. No. 3,329,557--Magat and Tanner, to use polyalkylene ethers of high molecular weight as a dispersed phase within the polymeric structure to improve the electrostatic properties of synthetic filaments. It is disclosed more specifically in U.S. Pat. No. 3,475,898 to Magat and Sharkey to use polyethylene-propylene ether glycols for the same purpose. Crovatt, Jr. in U.S. Pat. No. 3,388,104 discloses the use of the ethoxylated triglyceride of hydroxy stearic acid as an internal additive to polyamide fibers to modify their electrostatic propensity. In U.S. Pat. No. 3,366,731--Crovatt, Jr., discloses static resistant polyamide fibers containing the ethoxylated triglyceride of hydroxy stearic acid chain extended. In U.S. Pat. No. 3,860,671--Kowallik et al, disclose antistatic polyamide fibers containing a polyalkylene oxide reaction product. In U.S. Pat. No. 4,032,595--Fischer et al, disclose antistatic agents that are the reaction product of a polyalkoxylated triglyceride, of similar structure to that used by Crovatt, Jr., with an ester of oxalic or malonic acid. In U.S. Pat. No. 4,165,303, Schlossman et al, teach antistatic agents that are the mixed esters of polybasic acids and polyoxyalkylene glycols. In U.S. Pat. No. 3,755,497--Weedon et al, teach the use of propylene oxide-ethylene oxide copolymers based on ethylene diamine as antistatic agents when used in fibers of polyamide, polyester, polyurea, polyurethane or polysulfonamide; and in U.S. Pat. No. 4,108,922--Crescentini et al, disclose the use of Weedon's structure chain extended as an internal antistatic agent for polyamide fibers.
There are a number of disadvantages in use inherent in the prior art. For example, polyethylene glycols of sufficiently high molecular weight to be antistatic in effect when included inside the fiber are waxes with low melt viscosities which lead to difficulties in melt blending of the structure with molten polymer, which tend to allow agglomeration of the dispersed product phase in the molten polymer and separation of the dispersion from the polymer, thereby causing spinning drips. For improved performance they may require the use of thickening agents to increase their melt viscosities. Effective antistatic agents when dispersed in the fiber form rod-like particles after drawing of the fiber and in the case of low viscosity additives these rod-like particles tend to vary widely in diameter and length, thereby being less effective in antistatic action. Waxy, rod-like particles are known to break under normal conditions of drawing, and under flexing of fibers in their use in textile fabrics, thereby decreasing the effective length of the rods and concomitantly decreasing their effectiveness in anti-electrostatic activity.
In use of ethoxylated hydrogenated castor oils similar difficulties exist, it being a hard brittle wax of low melt viscosity at degrees of ethoxylation effective in obtaining antistatic properties. Chain extension with diglycidyl ethers or dibasic acid esters as taught by Crovatt, Jr. and by Fischer, to achieve higher melt viscosity does not ameliorate the brittleness of the structure.
Alkoxylated tetrols of the type disclosed by Weedon et al, and those chain extended as taught by Crescentini et al, are also waxes with the disadvantages inherent in such physical consistency. Further, an adverse effect has been observed in heavy denier polyamide fibers containing chain extended alkoxylated tetrols in comparison with the excellent crush resistance and recovery from crush of untreated polyamide fibers when tufted or woven into carpets and subjected to normal foot traffic in use as floor coverings.
Further, in structures such as those taught by Kowallik et al, the raw materials and reactions involved tend to provide a product which is economically questionable.